The higgs boson within and beyond the standard model

Abstract

The Standard Model (SM) of particle physics is based on the gauge group SU(3)C ×SU(2)L ×U(1)Y , which requires the eletroweak (EW) gauge bosons (W±,Z) to be massless. However, the masses of these bosons have been experimentally measured, which implies that the EW symmetry is spontaneously broken. This is done by incorporating the Higgs mechanism into the SM, which in turn predicts the existence of a neutral scalar Higgs boson. In July 2012 the CMS and ATLAS collaborations of the Large Hadron Collider (LHC) experiment at CERN announced the discovery of this Higgs boson. In this thesis, the SM, and the generation of fermion and gauge boson masses through the Higgs mechanism, is briefly reviewed. The properties of the Higgs boson as predicted by the SM, and the theoretical as well as the experimental limits on them from the Higgs boson searches at the Large Electron Proton (LEP) collider, the Tevatron, and the LHC are discussed in detail. Furthermore, since its discovery at the LHC, the subsequent developments in the measurements of the properties of the Higgs boson, such as its mass, interactions strengths and decay rates, are analysed. Finally, several open questions in high energy physics, such as the nature of dark matter (DM) and the baryon asymmetry of the universe, among others, hint at physics beyond the SM, which almost always predicts additional Higgs bosons. As a case study for new physics, we briefly revisit how the additional scalar Higgs boson of the two-Higgs-doublet model (2HDM) can manifest itself at the LHC and what implication does its existence carry for the Higgs boson already discovered.